A magnetic field or a magnetic flux may be detected by using a Hall Effect or XMR device (X-magneto-resistive sensor, e.g. AMR, GMR or TMR sensor). Thus, the Hall or XMR Effect device may be used for detecting a variation of a magnetic field, e.g. caused by a rotary motion of a camshaft wheel. Typically such a camshaft wheel has a notch or a tooth which influences the magnetic field of a fixed permanent magnet. This variation in the magnetic flux is found in an air gap between the permanent magnet and the passing camshaft wheel. Thus, the Hall or XMR Effect device provides a contactless monitoring of a speed or a position of a rotating element like a camshaft.
Hall Effect and XMR devices are based on the principle that a present magnetic field influences an output current or voltage in a magnetic field detecting element and thus a distribution of charged density across the magnetic field detecting element. This (asymmetric) distribution of the charge results in an electric potential across the magnetic field detecting element and in a voltage or a current, respectively. The voltage, also referred to as Hall voltage, provides information on the magnetic flux.
The signal of the Hall Effect device, e.g., a differential signal having a sine shape resulting from a motion of a camshaft wheel (where the maximum and the minimum of the sine signal correspond to a tooth and a notch of the wheel), may be digitally processed. Thus, the signal of the Hall or XMR Effect device is offset in order to compensate for effects like a temperature drift.